The present invention relates to silicone modified polyetherimides. More particularly, the invention relates to silicone modified polyetherimides having improved processing characteristics and mechanical properties.
Polyetherimides are unique polymers which exhibit superior physical and chemical properties, including high heat resistance, exceptional strength and excellent processability. These polymers can be used as wire coatings and are particularly suited for injection molding applications. Polyetherimides are conventionally made by reacting an aromatic bis(ether anhydride) with an organic diamine. Present manufacturing practices include solution polymerization or melt polymerization techniques or combinations of the two, as hereinafter described.
Polyetherimide resins are available commercially in the form of pellets. These pellets can be formed by fabrication into finished articles of widely varying shapes and sizes. Such articles are typically formed by extrusion or injection molding. Because of the high glass transition temperatures associated with polyetherimides, extrusion and injection molding requires elevated temperatures, and apparatus capable of withstanding large forces.
One means for reducing the forces required for extrusion and injection molding of conventional plastics is to incorporate lubricating compounds into the resin. Such lubricating compounds are thought to decrease frictional forces and also to modify the heat resistance of the resin. Throughput rates can be increased substantially by employing lubricating compounds, but the mechanical and physical properties of the plastic (such as strength and heat deflection temperature) are often adversely affected.
An important requirement for lubricants or flow modifiers to be used with polyetherimides is that they be resistant to elevated temperatures. As mentioned above, polyetherimides have high glass transition temperatures. This property is advantageous, because it permits the polymers to be used in high temperature applications. As a result of these high glass transition temperatures, processing temperatures are considerably higher for polyetherimides than for other plastics, and therefore, additives used with polyetherimides must have good heat resistance.
An additional requirement for lubricants and flow modifiers is that they be compatible with the polymer to which they are added. Such compatibility is evidence by clarity or homogeneity of the resulting plastic. Incompatible mixtures might be cloudy or contain streaks or blotches.
Silicone oils and gums have been used as flow modifiers or lubricants for polymers such as polyesters, polyethylene, polypropylene, polyvinylchloride and the like. Heretofore, the use of additives to improve the extrusion or injection molding characteristics of polyetherimides has not been reported.